Numerous useful processes are catalyzed by transition metal cationic complexes derived from a combination of a transition metal salt, a phosphine ligand, and a strong acid having a weakly or non-coordinating anion. Examples of such processes include hydroformylation of internal olefins, hydroformylation of .alpha.-olefins, acrylic acid produced from acetylene, copolymerization of olefins and carbon monoxide, and production of methyl propionate from ethylene. These cationic phosphine catalysts are typically stable in air, but phosphine precursors to these catalysts can be sensitive to exposure to air. Further, these catalysts have been prepared by multistep synthesis.
For example, U.S. Pat. No. 4,691,047 discloses a process for carbonylation of conjugated dienes with carbon monoxide and an alcohol or water in the presence of an aprotic solvent and a catalytic system prepared by combining a divalent palladium compound, a triarylphosphine and hydrochloric acid. U.S. Pat. No. 5,304,674 discloses an improvement to this process by adding a second diphosphine ligand having electron-releasing substituents on the phosphorus atoms.
European patent application 121,965 A2, 1984, discloses a process for copolymerization of ethylene with carbon monoxide in the presence of methanol using a catalytic system prepared by combining palladium acetate, a diphosphine and p-toluenesulfonic acid.
U. K. patent application 2,101,601A suggests a method to produce bisphosphines by preparation of the bisphosphonium salt followed by hydrolysis of the salt to yield the bisphosphine oxide and then reduction of the bisphosphine oxide to yield a bisphoshine. This method requires an additional process step; a relatively expensive reduction step.
It is therefore an object of the present invention to provide a process to produce a phosphonium salt that can be useful as a component of a catalyst system for reactions between carbon monoxides and olefinic hydrocarbons wherein reactants are not sensitive to exposure to oxygen, and wherein the number of process steps in the process is reduced.